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    Determining Confidence Intervals

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    In a recent study of 86 working adults, the mean number of hours per week spent talking on the phone was 21.6. The sd= 5.7 hours. Calculate the 90% confidence level for the mean.
    The format for writing a confidence interval is (xx.x, xx.x)

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    Please see the attachments.

    Since the sample is fairly large, we can use the normal distribution for the construction of CI.
    The confidence interval is given by , where = 21.6, σ = 5.7, n = ...

    Solution Summary

    The expert determines the confidence intervals for a study of working adults.